UPS systems having multiple operation modes and methods of operating same

ABSTRACT

A power supply system includes an AC input configured to be coupled to an AC source, an AC output configured to be coupled to a load, a UPS having an input coupled to the AC input and an output coupled to the AC output and a bypass circuit coupled between the AC input and the AC output and configured to open and close a bypass path therebetween. The system further includes a controller configured to control the UPS and the bypass circuit such that the UPS operates as an online UPS for a first input voltage magnitude condition at the AC input and as a standby UPS for a second input voltage magnitude condition at the AC input. A multi-mode converter may be coupled to a DC link of the UPS and configured to be selectively coupled to a battery and the AC input to respectively support battery conversion and current control at the AC input in respective first and second modes of operation of the UPS.

BACKGROUND OF THE INVENTION

The present invention relates to power supply apparatus and methods and,more particularly, to uninterruptible power supply (UPS) apparatus andmethods.

Any of a variety of different architectures may be used in a UPS,including online, standby and line interactive architectures. Such UPSarchitectures are described, for example, in U.S. Pat. No. 6,314,007 toJohnson.

A typical on-line UPS includes a combination of a rectifier and inverterlinked by a DC link. An AC utility source is typically coupled to therectifier, which responsively produces a DC voltage on the DC link. Theinverter typically generates an AC output voltage for a protected loadfrom the DC voltage on the DC link. An ancillary DC power source istypically coupled to the DC link to provide power to the inverter in theevent that the AC utility source fails.

Some online UPSs may include a bypass circuit, which may be used todirectly couple the AC utility source to the load. The bypass circuitmay be used, for example, for purposes of deactivating the rectifierand/or inverter for maintenance actions and/or to provide power to theload when the rectifier and/or inverter fails. Such a bypass circuit mayalso be used to provide a “high efficiency” mode of operation, asdescribed, for example, in U.S. Pat. No. 6,295,215 to Faria et al. Anonline UPS may also provide power conditioning (e.g., power factorcorrection) in a bypassed mode using the inverter and/or rectifier, asdescribed, for example, in U.S. Pat. No. 6,295,215 to Faria et al andU.S. Pat. No. 6,906,933 to Taimela.

A variety of techniques have been proposed for reducing input currentharmonic distortion and/or improving power factor for a UPS. Forexample, PCT International Application Publication WO 94/14228 toOughton describes techniques for operating a pulse width modulated (PWM)converter wherein occurrence of a notch portion of the input current tothe converter is determined, control signals are generated in responseto switch a plurality of bi-directional switches of the PWM converter sothat the input current is modified only during the notch portion. Thecurrent may be modified to a generally sinusoidal shape so that thetotal harmonic distortion of the input current is limited. U.S. Pat.Nos. 6,262,899, 6,400,586 and 6,661,678 to Raddi et al. describe variouspower factor correction circuits for UPS systems.

SUMMARY OF THE INVENTION

In some embodiments of the present invention, a power supply systemincludes an AC input configured to be coupled to an AC source, an ACoutput configured to be coupled to a load, a UPS having an input coupledto the AC input and an output coupled to the AC output and a bypasscircuit coupled between the AC input and the AC output and configured toopen and close a bypass path therebetween. The system further includes acontroller configured to control the UPS and the bypass circuit suchthat the UPS operates as an online UPS for a first input voltagemagnitude condition at the AC input and as a standby UPS for a secondinput voltage magnitude condition at the AC input. The first voltagemagnitude condition may include an input voltage at the AC input havinga magnitude greater than a predetermined threshold, and the second inputvoltage magnitude condition may include the input voltage at the ACinput having a magnitude less than the predetermined threshold. In someembodiments, the controller is configured to operate the UPS as a linecurrent conditioner when the UPS is operating as a standby UPS.

In further embodiments of the present invention, the UPS may include arectifier having an input coupled to the AC input, an inverter having anoutput coupled to the AC output, and a DC link coupling an output of therectifier to an input of the inverter. The UPS may further include abattery coupled to the DC link, and the controller may be configured tocause the inverter to provide current to charge the battery when the UPSis operating as a standby UPS. The UPS may further include a convertercoupling the battery to the DC link, and the controller be configured tooperate the converter to control current at the input of the UPS whenthe UPS is operating as an online UPS. The controller may also beconfigured to cause the inverter to regulate an AC voltage at the ACoutput when the UPS is operating as an online UPS.

According to further aspects of the present invention, a UPS includes anAC input, an AC output, a diode bridge rectifier having an input coupledto the AC input, an inverter having an output coupled to the AC output,and a DC link coupling an output of the rectifier to an input of theinverter. The UPS may further include a multi-mode converter coupled tothe DC link and configured to be selectively coupled to a battery andthe AC input to respectively support battery conversion and currentcontrol at the AC input in respective first and second modes ofoperation of the UPS.

The multi-mode converter may be configured to conduct current at the ACinput during selected periods of an AC voltage waveform at the AC input.The selected periods may include, for example, periods during whichdiodes of the diode bridge that couple the AC input to the DC link arereverse-biased. For example, the selected periods may include beginningand ending portions of half-cycles of the AC voltage waveform.

In further embodiments, the multi-mode converter includes a half-legcircuit including first and second transistors coupled in series betweenfirst and second busses of the DC link, an inductor coupled to a centertap of the half-leg circuit and configured to be coupled to the AC inputand a controller configured to control the first and second transistors.In some embodiments, the controller may be configured to operaterespective ones of the first and second switches in respective positiveand negative half cycles of the input voltage at the AC input when theinductor is coupled to the AC input. In some embodiments, the controllermay be configured to complementarily operate the first and secondtransistors during each of negative and positive half cycles of theinput voltage at the AC input when the inductor is coupled to the ACinput. The controller may be an open loop or closed loop controller.

Other embodiments of the present invention provide related methods ofoperating power supply systems and UPSs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates power supply apparatus and methods according tovarious embodiments of the present invention.

FIG. 2 illustrates power supply apparatus and methods according furtherembodiments of the present invention.

FIG. 3 illustrates a UPS including a multi-mode converter for batteryconversion and input current control according to additional embodimentsof the present invention.

FIGS. 4-6 illustrate exemplary operations of a multi-mode converter forbattery conversion and input current control according to additionalembodiments of the present invention.

FIGS. 7-8 illustrate control architectures for a multi-mode converterfor battery conversion and input current control according to additionalembodiments of the present invention.

DETAILED DESCRIPTION

Specific exemplary embodiments of the invention now will be describedwith reference to the accompanying drawings. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. The terminology used in the detailed description ofthe particular exemplary embodiments illustrated in the accompanyingdrawings is not intended to be limiting of the invention. In thedrawings, like numbers refer to like elements.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless expressly stated otherwise. Itwill be further understood that the terms “comprises,” “includes,”“comprising” and/or “including,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. It will be understood thatwhen an element is referred to as being “connected” or “coupled” toanother element, it can be directly connected or coupled to the otherelement or intervening elements may be present. Furthermore, “connected”or “coupled” as used herein may include wirelessly connected or coupled.As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Some embodiments of the present invention arise from a realization that,in some applications, such as information technology (IT) applications,the loads powered by UPSs may have power supplies that are capable ofpower factor correction and/or are tolerant of relatively wide voltageand frequency variations. Therefore, such loads may not require voltageand frequency regulation over a fairly significant envelope of inputvoltages. However, such loads still may require backup power and voltagemagnitude limitation, and may also benefit from line conditioning (e.g.harmonic suppression) even if their input voltage is not being tightlyregulated.

In some embodiments of the present invention, a UPS system includes aUPS, a bypass circuit and a controller that controls the UPS and bypasscircuit to provide an operational regime wherein the UPS operates as anonline UPS under a first condition of an input voltage magnitude at theAC input and as a standby UPS under a second condition of the inputvoltage magnitude at the AC input. For example, the UPS may operate asan online UPS when the AC input voltage magnitude of an AC sourceconnected thereto exceeds a threshold (e.g., a limit related to amaximum operating voltage of the load connected to the UPS), and the UPSmay operate as a standby UPS when the AC input voltage magnitude is lessthan this threshold. When operating from the AC source in the onlinemode, the UPS may operate to limit the voltage applied to the load.Using such an approach, it may be possible to provide higher powerdensity greater efficiency, as the system may operate in a moreefficient standby mode over a relatively large range of input voltageconditions. While powering the load on bypass from the AC source in thestandby mode, an inverter of the UPS may be used to provide lineconditioning and/or to provide charging current to the battery of theUPS.

FIG. 1 illustrates an UPS system 100 according to some embodiments ofthe present invention. The system 100 includes a UPS 101 including arectifier 110 (a diode bridge including a plurality of diodes D), aninverter 120 (including a plurality of insulated gate bipolartransistors (IGBTs) Q arranged in half-bridge circuits), a balancercircuit 130, a battery converter 140 and a battery 170. The rectifier110 is configured to produce positive and negative DC voltages +V_(DC),−V_(DC) on a DC link (rails) 112 a, 112 b (e.g., by charging storagecapacitors C) responsive to AC voltages applied to an input of therectifier 110. The inverter 120, under control of a controller 180, isconfigured to generate AC output voltages v′_(a), v′_(b), v′_(c) fromthe DC voltages +V_(DC), −V_(DC). Under control of the controller 180,the balancer circuit 130 regulates relative magnitudes of the DCvoltages +V_(DC), −V_(DC). The battery converter 140 provides power tothe DC link 112 a, 112 a from the battery 170 in a battery-powered modeof operation, and also is operative to provide charging current from theDC link 112 a, 112 b to charge the battery 170. The system 100 furtherincludes a bypass circuit 160 (here shown as including a plurality ofsemiconductor switches SCR), which is also controlled by the controller180. A contactor (relay) 150 is configured to couple and decouple thesystem 100 to and from an AC power source, here a three-phase utilitysource with phase voltages v_(a), v_(b), v_(c), under control of thecontroller 180.

According to some embodiments of the present invention, the controller180 may be configured to control the UPS 101 and the bypass circuit 160to provide and operational regime wherein the UPS 101 operates as anonline UPS under a first magnitude condition of the AC input voltagesv_(a), v_(b), v_(c), and as a standby UPS under a second magnitudecondition of the input voltage v_(a), v_(b), v_(c). For example, when amagnitude of the input voltages v_(a), v_(b), v_(c) is less than apredetermined threshold, for example, a threshold set to be near or lessthan a voltage magnitude limit for a load coupled to the inverter 120,power may be provided to the load by closing the bypass path through thebypass circuit 160, such that the AC input of the system 100 is directlycoupled to the load. In this operational mode, the UPS 101 can act as a“standby” UPS, i.e., the UPS 101 stands ready to supply power to theload from the battery 170, but does not regulate the voltages v′_(a),v′_(b), v′_(c) applied to the load, i.e., the inverter 120 does notregulate the output voltages v′_(a), v′_(b), v′_(c).

When supplying power from the AC source v′_(a), v′_(b), v′_(c) in thisstandby mode, the controller 180 may operate the inverter 120 as a lineconditioner, for example, in a manner similar to that described in theaforementioned U.S. Pat. No. 6,906,933 to Taimela, the disclosure ofwhich is incorporated by reference herein in its entirety. In addition,while operating from the AC source v_(a), v_(b), v_(c) in the standbymode, the controller 180 may also use the inverter 120 to supply currentto the DC link 112 a, 112 b and, thus, provide charging current to thebattery converter 140 for charging of the battery 170. In the event offailure of the AC input, the controller 180 may open the bypass pathusing the bypass circuit 160 and begin generating the AC output voltagesv′_(a), v′_(b), v′_(c), from the battery 170 using the battery converter140 and the inverter 120.

Responsive to a voltage magnitude of the AC input voltages v_(a), v_(b),v_(c) exceeding the aforementioned threshold while the UPS system 101 isin the standby mode, the controller 180 may transition to operating theUPS 101 in an online mode. In particular, the controller 180 may openthe bypass path using the bypass circuit 160, and may start generatingthe output voltages v′_(a), v′_(b), v′_(c) from the DC voltages +V_(DC),−V_(DC) using the inverter 120. In particular, in the online mode, thecontroller 180 may operate the inverter 120 such that the outputvoltages v′_(a), v′_(b), v′_(c) are maintained at a desirable levelbelow the threshold. While in this online mode, in response to a failureof the AC input to the rectifier 110, the controller 180 may directlytransition to battery-powered operation without re-closing the bypasscircuit 160. If the AC input returns, but at a level below theaforementioned threshold, the controller may close the bypass circuit160 and transition the UPS 101 to the standby mode of operation. If theAC input returns at a level above the threshold, the controller 180 maymaintain the UPS in the online mode.

It will be appreciated that, while FIG. 1 illustrates a three-phaseconfiguration, the present invention also includes single-phaseembodiments. A single-phase embodiment may, for example, use an inverterwith a single half-bridge and a rectifier with a single full orhalf-bridge. It will be understood that the controller 180 may beimplemented using any of a variety of different types of circuitry,including analog circuitry, digital circuitry (e.g., a microprocessor ormicrocontroller) or combinations thereof.

FIG. 2 illustrates a UPS system 100′ according to further embodiments ofthe present invention. The system 100′ includes many components shown inthe system 100 of FIG. 1, with like components indicated by likereference numerals. The system 100′ differs in that it includes a UPS101′ wherein the balancer circuit 130 and the battery converter 140 ofFIG. 1 are replaced by a combined battery converter/balancer 210, undercontrol of a modified controller 180′. It will be understood that thesystem 100′ may be operated in a manner similar to that described abovewith reference to FIG. 1.

According to further embodiments of the present invention, in a UPShaving a diode bridge rectifier, such as the rectifier 110 illustratedin FIG. 1, a multi-mode converter circuit may provide respective batteryconverter and input current control functions in respective first andsecond modes. In particular, in some embodiments of the presentinvention, the multi-mode converter may be configured to conduct currentat the AC input of the rectifier during selected periods of an ACvoltage waveform at the AC input when the rectifier and inverter of theUPS are operating in an online mode. The selected periods may be periodsduring which diodes of the diode bridge that couple the AC input to theDC link are reverse-biased. The selected periods may be beginning andending portions of half-cycles of the AC voltage waveform. Using such aconverter, crest factor, current harmonics (e.g., total harmonicdistortion (THD)) and/or neutral current may be reduced and input powerfactor may be increased, without requiring an undue number of additionalparts.

FIG. 3 illustrates a UPS 300 according to further embodiments of thepresent invention. The UPS 300 may be included in a UPS system along thelines of the UPS systems 100, 100′ of FIGS. 1 and 2. The UPS 300includes a diode bridge rectifier 310 including diodes D₁, D₂, . . . ,D₆. The UPS 300 also includes an inverter 320 coupled to the rectifier310 by a DC link (rails) 312 a, 312 b. The rectifier 310 and inverter320 may operate as described above.

The UPS 300 further includes a multi-mode converter 340 includinginsulated gate bipolar transistors (IGBTs) Q₁, Q₂, . . . , Q₆ arrangedas three parallel half-bridges, respective center taps of which arecoupled to respective input inductors L₁, L₂, L₃. The transistors Q₁,Q₂, . . . , Q₆ are controlled by a controller 380, which also controls aplurality of switches S₁, S₂, S₃ that selectively couple the respectiveinductors L₁, L₂, L₃ to a battery 370 and an input of the UPS where ACinput voltages v_(a), v_(b), v_(c), are applied.

In a first mode of operation, in particular, when the AC input hasfailed and the DC link voltages +V_(DC), −V_(DC) are being supported bythe battery 370, the switches S₁, S₂, S₃ couple the inductors L₁, L₂, L₃to the battery 370, and the controller 380 operates the multi-modeconverter 340 as a battery converter to produce output voltages v′_(a),v′_(b), v′_(c). In a second mode of operation, i.e., when the AC inputvoltages v_(a), v_(b), v_(c) are acceptable and the rectifier 310 isproviding current to the DC link 312 a, 312 b, the controller 380 causesthe switches S₁, S₂, S₃ to couple the inductors L₁, L₂, L₃ to the inputof the UPS 300 and operates the multi-mode converter 340 to controlinput current at the input of the UPS 300, so that, for example, theinput current may be shaped to provide better performance (e.g., reduceddistortion and/or improved power factor).

In particular, in some embodiments, the converter 340 may be used toconduct current at selected portions of the input voltage waveform,while using the diodes of the rectifier 310 to conduct current duringother portions of the input voltage waveform. Referring to FIG. 4, whichshows control for phase A, the transistors Q1, Q4 may be pulse widthmodulated during sectors I, II, III, IV during half-cycles of the phaseA voltage v_(a) to provide controlled current flow at the input of theUPS 300 during, for example, portions of the AC input voltage waveformin which the phase A diodes D₁, D₄ are reversed-biased and, thus,non-conducting. In central portions of the voltage half cycles, theconverter 340 may be deactivated (i.e., turn both Q₁ and Q₄ off) and,during this interval, current may flow through the phase A diodes D₁, D₄during periods in which the magnitude of the input phase A voltage v_(a)exceeds the magnitude of the corresponding positive or negative DC linkvoltage +V_(DC), −V_(DC) and the diodes D₁, D₄ are forward biased. Underlight loading, the sectors I, II, III, IV may merge.

Still referring to FIG. 4, controllable variables for the sectors I, II,III, IV include peak currents h1, h2, duration of ramp-up and ramp-downperiods t1, t3, t4, t6, and duration of controlled current magnitudeperiods t2, t5. Current during one of these periods, such as the ramp-upperiod t1, the controller 380 may cause the input current to conform toa line or curve with a desired prescription. The variables may bedetermined by load, inductor rating, and other parameters. Thecontroller 380 may operate the converter 340 using open loop and/orclosed loop techniques, e.g., the controller 380 may operate responsiveto the input voltage and current sensed in the input inductor (e.g.,inductor L₁). It will be understood that the controller 380 may beimplemented using any of a variety of different types of circuitry,including analog circuitry, digital circuitry (e.g., a microprocessor ormicrocontroller) or combinations thereof.

In some embodiments of the present invention, current control by aconverter along the lines of the converter 340 may be achieved using a“unipolar” switching regime. Referring to FIG. 5 in combination withFIG. 3, during a positive half cycle of the phase A voltage v_(a), thelower transistor Q₄ is modulated while keeping the upper transistor Q₁off. During this half-cycle, when the lower transistor Q₄ is turned on,current builds up through the inductor L₁. When the lower transistor Q₄is turned off, current flows to the upper DC rail 312 a via the bodydiode of the upper transistor Q₁ and/or the rectifier diode D₁. Duringthe negative half-cycle of the phase A voltage v_(a), the uppertransistor Q₁ is modulated while keeping the low transistor Q₄ off.During this half-cycle, when the upper transistor Q₁ is turned on,current builds up through the boost inductor L₁. When the uppertransistor Q₁ is turned off, current flows from the lower DC rail 312 bvia the body diode of the lower transistor Q₄ and/or the rectifier diodeD₄. It will be appreciated that similar operations may be performed forphases B and C.

In further embodiments of the present invention, current control by aconverter along the lines of the converter 340 may be achieved using a“complementary” switching regime. Referring to FIG. 6 in relation toFIG. 3, during a positive half cycle of the phase A voltage v_(a), thelower transistor Q₄ and the upper transistor Q₁ are complementarilymodulated. During this half-cycle, when the lower transistor Q₄ isturned on, current builds up through the boost inductor L₁. When thelower transistor Q₄ is turned off and the upper transistor Q₁ is turnedon, current flows to the upper DC rail 312 a via the upper transistorQ₁. Similarly, during the negative half-cycle of the phase A voltagev_(a), the upper transistor Q₁ and the lower transistor Q₄ arecomplementarily modulated. During this half-cycle, when the uppertransistor Q₁ is turned on, current builds up through the inductor L₁.When the upper transistor Q₁ is turned off and the lower transistor Q₄is turned on, current flows to the lower DC rail 312 b via the lowertransistor Q₄.

FIGS. 7 and 8 illustrate exemplary closed-loop control structures forcurrent control using a complementary switching techniques along thelines described above according to further embodiments of the presentinvention. Referring to FIG. 7, a pulse width modulation control loopincludes input analog to digital (A/D) and scaling circuitry 710, whichreceives phase voltage, phase current and DC link voltage signalsv_(AC), i_(AC), V_(DC) and generates corresponding digital phasevoltage, phase current and DC link voltage signals v_(AC)′, i_(AC)′,V_(DC)′. The digital DC link voltage signal V_(DC)′ is provided to asumming junction 720, where it is compared with a DC link voltagereference signal V_(DCref). The error signal generated from thecomparison is applied to a DC link voltage loop compensator 730, whichresponsively generates a current reference signal i_(ref) that isprovided to a current regulator 740. The current regulator 740 alsoreceives the digital phase voltage, phase current and DC link voltagesignals v_(AC)′, i_(AC)′, V_(DC)′. Responsive to these inputs, thecurrent regulator 740 generates a pulse-width modulation command signal745 that is provided to a pulse-width modulator (PWM) 750. The PWM 750responsively generates control signals 755 a, 755 b, which may be drivesignals applied, for example, to upper and lower transistors of ahalf-leg circuit of a converter, such as the converter 340 of FIG. 3. Itwill be appreciated that a control structure along the lines shown inFIG. 7 may be provided for each phase in multi-phase applications.

FIG. 8 illustrates an exemplary configuration for the current regulator740. The current regulator 740 includes gain blocks 805, 810, 815, 820that receive respective ones of the input digital phase voltage, phasecurrent and DC link voltage signals v_(AC)′, i_(AC)′, V_(DC)′ and thecurrent reference signal i_(ref). Scaled versions of the input digitalphase voltage and DC link voltage signals v_(AC)′, V_(DC)′ are appliedto a divider 825, producing a signal that is applied to a summingjunction 850. Scaled versions of the input digital phase voltage signalv_(AC)′ and the current reference signal i_(ref) are provided to amultiplier 830, which produces a reference signal that is applied to alimiter 832, which produces a limited signal that is applied to asumming junction 835. At the summing junction 835, and offset signalv_(offset) is added, and the resulting signal is provided to anothersumming junction 840, where it is compared with a scaled version of thephase current signal i_(AC)′. The error signal produced by the summingjunction 840 is provided to a current loop compensator 845, whichproduces a command signal that is summed with the output of the divider825 at the summing junction 850. The composite command signal producedby the summing junction 850 is limited by a limiter 860, producing thepulse-width modulation command signal 745.

The control architectures shown in FIGS. 7 and 8 are provided forpurposes of illustration, and it will be appreciated that otherclosed-loop and open-loop control structures may be used in otherembodiments of the present invention. It will be further appreciatedthat control structures for embodiments of the present invention may beimplemented using any of a variety of different types of electroniccircuits, including analog circuits, digital circuits (e.g.,microprocessors and microcontrollers), and combinations thereof.Embodiments of the present invention include single-phase andmulti-phase implementations.

In the drawings and specification, there have been disclosed exemplaryembodiments of the invention. Although specific terms are employed, theyare used in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being defined by the followingclaims.

1. A power supply system comprising: an AC input configured to becoupled to an AC source; an AC output configured to be coupled to aload; a UPS having an input coupled to the AC input and an outputcoupled to the AC output, wherein the UPS comprises a rectifier havingan input coupled to the AC input, an inverter having an output coupledto the AC output, a DC link coupling an output of the rectifier to aninput of the inverter, and a battery coupled to the DC link; a bypasscircuit coupled between the AC input and the AC output and configured toopen and close a bypass path therebetween; and a controller configuredto control the UPS and the bypass circuit such that the UPS operates asan online UPS for a first input voltage magnitude condition at the ACinput and as a standby UPS for a second input voltage magnitudecondition at the AC input, wherein the controller is configured tooperate the UPS as an online UPS by transferring power from the AC inputto the AC output via the rectifier and the inverter in a first onlineUPS operation state and transferring power from the battery to the ACoutput via the inverter in a second online UPS operation state, andwherein the controller is configured to operate the UPS as a standby UPSby transferring power from the AC input to the AC output via the bypasscircuit in a first standby UPS operation state and transferring powerfrom the battery to the AC output via the inverter in a second standbyUPS operation state.
 2. A method of operating a power supply systemincluding an AC input configured to be coupled to an AC source, an ACoutput configured to be coupled to a load, a UPS having an input coupledto the AC input and an output coupled to the AC output, and a bypasscircuit coupled between the AC input and the AC output and configured toopen and close a bypass path therebetween wherein the UPS comprises arectifier having an input coupled to the AC input, an inverter having anoutput coupled to the AC output, a DC link coupling an output of therectifier to an input of the inverter, and a battery coupled to the DClink, the method comprising: controlling the UPS and the bypass circuitsuch that the UPS operates as an online UPS for a first input voltagemagnitude condition at the AC input and as a standby UPS for a secondinput voltage magnitude condition at the AC input, wherein controllingthe UPS and the bypass circuit such that the UPS operates as an onlineUPS for a first input voltage magnitude condition at the AC input and asa standby UPS for a second input voltage magnitude condition at the ACinput comprises: operating the UPS as an online UPS by transferringpower from the AC input to the AC output via the rectifier and theinverter in a first online UPS operation state and transferring powerfrom the battery to the AC output via the inverter in a second onlineUPS operation state; and operating the UPS as a standby UPS bytransferring power from the AC input to the AC output via the bypasscircuit in a first standby UPS operation state and transferring powerfrom the battery to the AC output via the inverter in a second standbyUPS operation state.